The present invention refers to a hybrid pinion bearing unit for use in a motor vehicle front axle differential with negative hypoid offset and also for motor vehicle power transfer units, and the purpose is to provide an application-oriented optimization of the bearing assembly of the pinion shafts in drivelines. In relation to the present drivelines, due to the more and more increasing negative hypoid offset (i.e. the rotational axis of the differential is situated below the corresponding pinion shaft) in the future, in front axle differentials and the conversion of the helical directions associated therewith of the taper drive, the force conditions in the hypoid gearing will also change. Thereby the pinion axle in tractive operation in the future will be pulled into the crown wheel gears. In order to still be able to obtain such a low clearance of the flank of a tooth as possible, it is above all necessary to have a bearing assembly which is optimized for stiffness in axial direction.
Corresponding conditions are at hand at the so called PTUs (power transfer units) for all-wheel driven vehicles, at which the driven pinion axle via the crown wheel transfers its force to the driven driving element, and consequently the axial force has the same effect as described above.
In both cases the force conditions in the tooth engagement between crown wheel and pinion as compared to the conditions which are today common in rear wheel drives, differ thereby that the bearing unit according to the present invention is intended to make it possible to obtain an evident improvement regarding bearing stiffness with a simultaneous clear reduction of the effect of bearing losses.
U.S. Pat. No. 4,729,252 discloses a bearing unit for a pinion gear shaft incorporating a taper roller bearing and an angular ball bearing having a common outer race ring and separate, axially spaced apart inner race rings, and it is stated that the contact lines of the taper roller bearing intersect each other at an angle of less than 90° and that the contact lines of the balls of the angular ball bearing likewise intersect each other at an angle of less than 90°.
The stiffness of such a bearing combination is not optimal in view of the different characteristics for a taper roller bearing and an angular ball bearing.
The purpose of the present invention is therefore to propose a modified bearing unit of this type, whereby the above problems are eliminated, and this is achieved by the invention disclosed and claimed hereinafter.